1. Field of the Invention
THIS INVENTION relates to a brake or damper assembly. The invention is particularly suitable for, but not limited to, a shovel dipper door brake.
2. Description of the Prior Art
At present, to control the swinging motion of the dipper door, manufacturers utilise snubber brakes.
These snubber brakes are mechanically connected to the door by link arms which, when the door opens and closes, transfer the door movement to two or more friction plates. These friction plates move fore and aft in the snubber assembly.
The snubber assembly consists of two fixed end friction plates, friction discs, a separator plate and two moving friction plates.
To create the braking effect on the door, the above components are pre-loaded by an adjusting nut, preloading a number of Belleville washers. The door is constantly under a braking effect during any motion, while all components are serviceable and correctly adjusted.
Failure to achieve the braking effect will cause the door to swing in an uncontrolled manner during the opening and closing operation.
Uncontrolled motion of the door will cause damage to the door and to the maximum travel stops during the opening travel, and will cause extensive damage to the door structure, latch bar, latch bar box and dutchman during the closing travel.
This mechanism is very susceptible to most types of climactic conditions, be it dry and dusty, wet, muddy, etc. and as a result, requires constant monitoring and adjustment which is labour intensive. Over adjustment will cause excessive component wear and under adjustment will result in dipper door and dipper component cracking and fatigue.
In some operations, adjustment could be as regular as once per day, resulting in considerable down time and loss of production. The adjustment time could be in the order of 30 to 40 minutes per shovel per day.
It will be stated by manufacturers that "our shovels do not require adjustment on a daily basis", and true, not all do, but on scheduled maintenance days, additional labor is required to carry out crack repairs, etc., to the door, which can be directly attributed to the poorly adjusted snubber brakes.